Molecular genetics

Question 1

Define DNA

Answer 1

DNA is the genetic material that organisms inherit from their parents, and carries genetic code (genes), used for synthesising specific polypeptides

Question 2

Define a chromosome

Answer 2

A chromosome is a DNA molecule condensed during cell division

Question 2

What does a nucleotide consist of

Answer 2

• Phosphate group
• Deoxyribose sugar
• Nitrogenous base

Question 3

How is the sugar phosphate backbone of a DNA molecule formed

Answer 3

Sugar phosphate backbone is formed when the phosphate group of one nucleotide joins with the deoxyribose sugar of the next nucleotide

Question 3

What is the shape of the phosphate group

Answer 3

Circular

Question 3

What is the shape of the deoxyribose sugar

Answer 3

Pentagon

Question 4

What are the rules for complementary base pairing

Answer 4

• Adenine forms double hydrogen bonds with thymine
• Cytosine forms triple hydrogen bonds with guanine

Question 5

Describe the process of DNA replication

Answer 5

• DNA replicates following the process of semi-conservative replication
• Each polynucleotide strand of original DNA acts as a template for the synthesis of a new complementary polynucleotide strand
• Original double helix first separated by enzymes
• Nucleotides are bound to separated polynucleotide strands following rules of complementary base pairing with the aid of enzymes
• Results in the formation of 2 double-stranded DNA molecules

Question 5

What are the nitrogenous bases

Answer 5

• Adenine
• Thymine
• Guanine
• Cytosine

Question 6

Define a gene

Answer 6

A gene is a unit of inheritance with a specific sequence of nucleotides, as part of a DNA molecule that contains the information to make a polypeptide

Question 7

How does genetic information flow

Answer 7

DNA > RNA > Protein

Question 8

Define transcription

Answer 8

Transcription is when the message in the gene is copied into an mRNA in the nucleus

Question 9

Describe how polypeptides are synthesised

Answer 9

• In nucleus, message in gene is copied into an mRNA through process of transcription
• mRNA travels to cytoplasm and attaches itself to a ribosome
• Ribosome moves along the mRNA and synthesises a polypeptide through process of translation
• Polypeptide is released when ribosome leaves the mRNA

Question 9

Define translation

Answer 9

Translation is the synthesis of a polypeptide chain from mRNA

Question 10

How many bases on the mRNA make up a codon

Answer 10

3

Question 11

What happens when a change occurs to the nucleotide sequence

Answer 11

• Type of amino acids on the chain changes
• Structure of protein changes
• Protein loses its function

Question 11

When is a polypeptide chain functional

Answer 11

When it folds into a specific 3D shape

Question 11

How many amino acids does a codon code for

Answer 11

1

Question 11

What determines the sequence of amino acids in a protein

Answer 11

Order of nucleotide bases

Question 12

What are the similarities between DNA and mRNA

Answer 12

• Both have a sugar phosphate backbone
• Both have 3 common nitrogenous bases

Question 13

What is the structure of DNA

Answer 13

• 2 strands
• Double helix structure
• Deoxyribonucleotide monomer
• Deoxyribose sugar as the pentose sugar
• Contains thymine
• Hydrogen bonds between bases

Question 14

What is the structure of mRNA

Answer 14

• 1 strand
• Straight chain structure (Mostly)
• Ribonucleotide monomer
• Ribose sugar as pentose sugar
• Contains uracil
• No hydrogen bonds if it is a straight chain structure

Question 15

Define down syndrome

Answer 15

Down syndrome is caused by the non-separation of chromosome 21 in meiosis during gamete formation, resulting in the zygote having an extra chromosome 21, so body cell ends up with 47 chromosomes instead of 46

Question 15

Define mutation

Answer 15

Mutation is a spontaneous or induced change in the DNA sequence of genes, or a change in the number or structure of chromosomes

Question 16

Define mutagens

Answer 16

Mutagens are physical or chemical agents that can cause alterations to DNA, resulting in changes in the sequence of DNA

Question 17

What is genetic engineering

Answer 17

Genetic engineering is used to transfer genes from one organism to another by using a vector

Question 17

Describe sickle cell anaemia

Answer 17

- Sickle cell anaemia caused by a gene mutation, resulting in a substitution of a single amino acid in the haemoglobin protein - Sickle cell haemoglobin molecules aggregate into long rods that deform the cells into a sickle shape

Question 18

What is a vector

Answer 18

A vector carries the genes to the intended cells

Question 19

What are plasmids

Answer 19

Circular strands of DNA that replicate separately from bacterial DNA

Question 19

Why are bacteria used to produce insulin

Answer 19

- Easy to transfer genes into bacteria - Bacteria contain plasmids, in which insulin genes can be inserted easily - Bacteria take a short time to replicate

Question 20

What is a restriction enzyme

Answer 20

A restriction enzyme is an enzyme that cuts the 2 ends of a gene to produce 'sticky ends'

Question 21

Describe how a human insulin gene is inserted into bacterial DNA

Answer 21

- Cut the human insulin gene with a restriction enzyme, producing 'sticky ends' - Each 'sticky end' is a single strand sequence of DNA bases, which can pair with complimentary bases to form a double strand - Obtain a plasmid from a bacterium and cut the plasmid open with the same restriction enzyme, producing 'sticky ends' complementary to ends of insulin gene - Mix plasmid with DNA fragment containing insulin gene - DNA fragment with insulin gene will bind to plasmid by complementary base pairing of the 'sticky ends' - Add DNA ligase to seal DNA fragment to plasmid, forming a recombinant plasmid - Mix plasmid with bacterium - Apply heat or electric shock to open cell membrane for plasmid to enter - Transgenic bacterium will synthesise insulin together with other proteins from plasmid - Insulin must be extracted and purified before use